Differential effects of dexamethasone on the thymus and spleen: alterations in programmed cell death, lymphocyte subsets and activation of T cells

The kinetics of DEX-induced changes in lymphocytes from the thymus and spleen of normal mice were examined in relation to cell numbers, programmed cell death (PCD), in vitro proliferative response to anti-CD3 antibodies or Con-A, and changes in lymphocyte subsets by flow cytometry. The above aspects were examined at 48, 24, 18, and 3 h after a single intraperitoneal injection of DEX. Profound reduction of thymocyte numbers was noticed particularly at 48 (74-84%) and 24 (43-55%) h after DEX administration. PCD of thymocytes was not detectable at 48 h, marginally detectable at 24 h, markedly evident at 18 h, and minimally detectable at 3 h pi of DEX. PCD in splenic lymphocytes of DEX-treated mice was not clearly evident at these time points. Thymocytes from mice exposed to DEX (48 or 24 h) proliferated vigorously when cultured in the presence of anti-CD3 or Con-A, thereby suggesting that the remaining thymocytes can transduce activation signals. In contrast, splenic lymphocytes from the same animals responded poorly to these stimulants. Flow cytometric studies revealed that there was a marked increase in number of thymocytes expressing CD3+ (4-6 fold) and alpha beta TCR+ (2-7 fold) surface molecules. On the other hand, no major changes in CD3+ or alpha beta TCR+ cells were noticed in the spleen of DEX-treated mice. Although the total numbers of cells expressing heat stable antigen, M1/69, were not markedly altered after DEX treatment, the fluorescent intensity profile was modified. There were no remarkable changes in CD45RB+ cells in these mice. CD44+ cells were not decreased in DEX-treated thymocytes or splenic lymphocytes. Our results suggest that DEX has differential effects on the thymus and the spleen.

Aliphatic alcohols stabilize an alternative conformation of the tryptophan synthase alpha 2 beta 2 complex from Salmonella typhimurium

The conformational changes that accompany association of the tryptophan synthase alpha and beta 2 subunits are probed by investigating the effects of solvents on the catalytic and spectroscopic properties of tryptophan synthase. Low concentrations of ethanol, propanol, and butanol inhibit conversion of L-serine and indole to L-tryptophan by the alpha 2 beta 2 complex. Inhibition depends on the concentration, chain length, and hydrophobicity of the alcohol. In contrast, these alcohols increase the rates of conversion of beta-chloro-L-alanine and indole to L-tryptophan and of L-serine to pyruvate. Thus, alcohols alter the substrate specificity and reaction specificity of the alpha 2 beta 2 complex. These altered specificities are similar to those of the free beta 2 subunit in aqueous solution. The spectroscopic properties of enzyme-substrate intermediates formed by the alpha 2 beta 2 complex in 3 M ethanol and 0.5 M 1-butanol also resemble the intermediates formed by the free beta 2 subunit in aqueous solution. Experiments using gel-filtration, membrane ultrafiltration, and limited proteolysis show that the alpha 2 beta 2 complex does not dissociate at low concentrations of alcohols. Our results provide evidence that alcohols can stabilize an alternative conformation of the alpha 2 beta 2 complex which is similar to the open conformation of the free beta 2 subunit in aqueous solution.

Effect of multiple light scattering and self-absorption on the fluorescence and excitation spectra of dyes in random media

The absorption, fluorescence, and excitation spectra of a dye in a highly scattering random medium were studied experimentally. The intrinsic absorption spectrum of the dye does not change in the presence of scatterers, but the presence of scatterers in the media will change the observed fluorescence spectra. The observation is accounted for by the change in the photon trajectory path length for the fluorescence emission.

A new rapid and simple non-radioactive assay to monitor and determine the proliferation of lymphocytes: an alternative to [3H]thymidine incorporation assay

A one-step non-radioactive assay to determine the proliferation of murine lymphocytes, lymphoid tumor cells and hybridoma cells is described. This assay requires the addition of Alamar Blue dye to cell cultures and the degree of change in its color, which is reflective of the extent of cellular proliferation, can be determined by an ELISA plate reader. Alamar Blue must be added during the initial phase of cell culture. The pattern of concanavalin A (ConA) or anti-CD3 antibody-induced proliferative response of murine lymphocytes as assessed by Alamar Blue was similar to that of a [3H]thymidine assay. Similarly, the spontaneous proliferation curve of anti-CD3 antibody secreting cell line (YCD3-1), monocytic macrophage cell lines (PU5-1.8, P388D1, J774.1) and myeloma cells (Sp2/0) as determined by Alamar Blue closely resembled that of the [3H]thymidine assay. The minimum detectable number of proliferating cells was comparable in Alamar Blue and [3H]thymidine assays. Since cell lysis/extraction and washing procedures are not involved in the Alamar Blue assay, this approach has several distinct advantages over currently available assays (eg. [3H]thymidine). First, it allows daily monitoring of proliferation without compromising the sterility of cultures. An indication of proliferation can be evaluated (spectrophotometrically or visually) as early as 24 h after ConA stimulation. Second, unlike previously reported assays, Alamar Blue permits further analysis of proliferating cells by other methods. Analysis of cells in culture with Alamar Blue for various surface antigens (CD44, CD45RB, CD4, heat stable antigen) by flow cytometry revealed that the fluorescent profile and relative percentage of cells in cultures with the Alamar Blue were comparable to those without this reagent. The salient advantages of Alamar Blue assay over the [3H]thymidine assay include: (i) non-radioactivity; (ii) simplicity; (iii) less costly; (iv) non-labor intensive; (v) rapidity of assessment of proliferation of large number of samples; (vi) non-toxicity; (vii) usefulness in determining the kinetics of cell growth of hybridomas; and (viii) non-interference of secretion of antibodies by a hybridoma cell line.

Antibodies to cardiolipin in normal C57BL/6J mice: induction by estrogen but not dihydrotestosterone

Autoantibodies against cardiolipin, a phospholipid, have been demonstrated in a variety of pathological states including several autoimmune conditions in humans and in certain lupus-prone mice. In this study we detected antibodies reactive to cardiolipin in normal C57BL/6J mice by ELISA. The autoantibodies are detected less frequently in the serum of male than in female mice, suggesting the influence of sex hormones. The relative refractoriness of normal male mice to the induction of anticardiolipin antibodies is not due to the suppressive effects of male hormones, since prepubertal orchiectomy has little influence on this autoantibody. Further, dihydrotestosterone treatment of orchiectomized mice has minimal effect on anticardiolipin antibodies. However, orchiectomized mice when given estrogen develop a marked increase in the incidence as well as the levels of these autoantibodies. Similarly, estrogen treatment of female mice further augments the incidence and the levels of these autoantibodies. Estrogen-treated mice also have antibodies reactive against other membrane phospholipids including phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The intensity of binding of autoantibodies to the above phospholipids varies among individual mice. To our knowledge, this is the first report on the demonstration of antiphospholipid autoantibodies in normal mice and induction of these antibodies by estrogen.

By toxic effects of the dried leaves and stem of Capparis tomentosa on Nubian goats

Nubian goats were given single or repeated dosages of 5, 2.5 and 0.25 g/kg of dried leaves or stem of C. tomentosa by drench and died or were slaughtered at various times post-dosing. One goat receiving Capparis stem at 2.5 g/kg on every other day basis for 8 days developed signs of toxicosis and recovered following cessation of plant administration. The prominent features of toxicity were inappetence, locomotor disturbances, paresis especially of the hind limbs and recumbency. Lesions comprised perineuronal vacuolation in the gray matter of the spinal cord at the sacral region, centrilobular hepatocellular necrosis, degeneration of the renal proximal convoluted and collecting tubules, serous atrophy of the cardiac fat and renal pelvis and straw-coloured fluid in serious cavities. In Capparis-fed goats, anaemia developed and the results of kidney and liver function tests were correlated with clinical abnormalities and pathologic changes.

Catalytic properties of streptococcal NADH oxidase containing artificial flavins

The flavoprotein NADH oxidase from Streptococcus faecalis 10C1, which catalyzes the tetravalent reduction of O2-->2H2O, has been purified as the apoenzyme to allow reconstitution studies with both native and artificial flavins. Turnover numbers for the enzyme containing 1-deaza-, 2-thio-, and 4-thio-FAD range from 51 to 4% of that of the native FAD enzyme; these reconstituted oxidases also catalyze the four-electron reduction of oxygen. Dithionite and NADH titrations of the native FAD oxidase require 1.7 eq of reductant/FAD and follow spectral courses very similar to those previously reported for the purified holoenzyme. Azide is a linear mixed-type inhibitor with respect to NADH, and dithionite titrations in the presence of azide yield significant stabilization of the neutral blue semiquinone. Redox stoichiometries for the oxidase containing modified flavins range from 1.1 to 1.4 eq of reductant/FAD. Spectrally distinct reduced enzyme.NAD+ complexes result with all but the 2-thio-FAD enzyme on titration with NADH. The reduced 4-thio-FAD oxidase shows little or no evidence of desulfurization to native FAD on reduction and reoxidation. Both the 8-mercapto- (E'o = -290 mV) and 8-hydroxy-FAD (E'o = -335 mV) oxidase are readily reduced by excess NADH. These results offer a further basis for analysis of the active-site structure and oxygen reactivity of this unique flavoprotein oxidase.

Potential and limitations of energy-transfer processes in pulsed and cw dye laser mixtures: comparison of theory and experiments

A comprehensive energy-transfer dye laser (ETDL) simulation model and the premise on which it is based are examined and reviewed. The model permits theoretical predictions of the total transfer efficiency and hence identification of the appropriate mechanisms that are responsible for energy transfer as well as predicting fluorescence spectra of dye mixtures. Using concentration regimes that are generally applicable to laser action, we also show that the model is capable of predicting gain line shapes (and hence tunability) for pulsed ETDL's. An extension of the model also predicts the gain spectrum of cw laser-pumped ETDL's as a function of donor and acceptor concentrations, their spectral data, energytransfer parameters, pump power and wavelength, and dimensions of the active region. Model simulation results are checked against experimental results for pulsed and cw ETDL's with laser outputs in the visible and near-IR spectral regions. The results lead to a better and more detailed understanding of ETDL mec hanisms and the role that the triplet states play in these mechanisms.

Evidence for two conformers of the beta subunit of tryptophan synthase in solution

To explain our finding that the dimeric beta subunit of tryptophan synthase is only 50% inactivated by beta-chloro-L-alanine (Ahmed, S. A., Ruvinov, S. B., Kayastha, A. M., and Miles, E. W. (1991) J. Biol. Chem. 266, 21548-21557), we have extended our investigation using spectroscopic, steady-state kinetic, and electrophoretic methods. The spectroscopic properties of the half-active beta 2 dimer and the reactivation after alkali treatment show that the inactivation proceeds by an "enamine" mechanism. Although the fully active beta 2 dimer associates with the tryptophan synthase alpha subunit to form alpha 2 beta 2 complex, the inactive beta subunits in the half-active enzyme associate weakly or not at all with the alpha subunit. Our results provide evidence for two conformers of the beta subunit in solution: one is rapidly inactivated by beta-chloro-L-alanine and the other is not inactivated. Thermal inactivation studies and non-denaturing polyacrylamide gel electrophoresis of the half-active enzyme show that the beta 2 dimer exists in both homologous and heterologous combinations of these two forms. After removal of the reaction products and unreacted beta-chloro-L-alanine from the half-active beta 2 dimer by gel filtration, further incubation with beta-chloro-L-alanine results in the loss of 50% of the remaining activity. This result suggests that the subunits undergo rearrangement via an intermediate monomer form to regenerate the two conformers of the active beta subunit. This mechanism of rearrangement is supported by our finding that the extent of inactivation increases at lower concentrations of the beta 2 dimer.

Experimental verification of a theoretical model for continuous wave energy transfer dye mixture lasers in the near infrared

We report the experimental verification of a simulation model for cw energy transfer dye lasers. Experimentals results obtained with Rhodamine 610 (donor) and Nile Blue 690 (acceptor) confirm theoretical model predictions.

Active-site structural comparison of streptococcal NADH peroxidase and NADH oxidase. Reconstitution with artificial flavins

The apoproteins of the streptococcal NADH peroxidase (H2O2----2H2O) and NADH oxidase (O2----2H2O) stabilize the neutral forms of 6-hydroxy- and 6-mercapto-FAD, respectively. The redox behavior of the 6-hydroxy-FAD peroxidase closely mimics that of the native enzyme with both dithionite and NADH. Both oxidase and peroxidase preferentially stabilize the N(1)-protonated p-quinonoid species of 8-mercapto-FAD, and the 8-position of the bound flavin is accessible to solvent in both proteins. The 8-mercapto-FAD peroxidase yields an EH2 spectrum on reduction virtually identical to that seen with 8-mercapto-FAD glutathione reductase, but no distinct EH2.NADH form appears. The dramatic decreases in reactivity at the flavin 2- and 4-positions for both the peroxidase and the oxidase, assessed with the reconstituted 2- and 4-thio-FAD enzymes, suggest that these positions are buried by elements of both protein structures. Furthermore, reconstitution of the peroxidase with the higher potential 2- and 4-thioflavins yields enzyme forms which are fully reducible with 1.4 eq of NADH/FAD, giving rise to stable thio-FADH2.NAD+ complexes. This behavior closely mimics that of the native NADH oxidase and provides further evidence supporting the hypothesis that a major functional distinction between the two structurally related proteins is determined by the redox potential and/or NADH reactivity of the bound flavin coenzyme.

Biosynthetic-Studies on Tajixanthone and Shamixanthone, Polyketide Hemiterpenoid Metabolites of Aspergillus variecolor

The biosynthesis of tajixanthone and related metabolites of Aspergillus variecolor has been studied by incorporation experiments with simple and advanced precursors labelled with the stable isotopes 13C, 2H and 18O. Tajixanthone is shown to be derived through ring cleavage of an octaketide -derived anthraquinone with introduction of two dimethylallyl moieties. From the results of isotopic labelling experiments and chemical studies on model compounds, an overall biosynthetic pathway is proposed and information on the mechanisms of interconversion of proposed intermediates is obtained.

Mechanism of mutual activation of the tryptophan synthase alpha and beta subunits. Analysis of the reaction specificity and substrate-induced inactivation of active site and tunnel mutants of the beta subunit

The origin of reaction and substrate specificity and the control of activity by protein-protein interaction are investigated using the tryptophan synthase alpha 2 beta 2 complex from Salmonella typhimurium. We have compared some spectroscopic and kinetic properties of the wild type beta subunit and five mutant forms of the beta subunit that have altered catalytic properties. These mutant enzymes, which were engineered by site-directed mutagenesis, have single amino acid replacements in either the active site or in the wall of a tunnel that extends from the active site of the alpha subunit to the active site of the beta subunit in the alpha 2 beta 2 complex. We find that the mutant alpha 2 beta 2 complexes have altered reaction and substrate specificity in beta-elimination and beta-replacement reactions with L-serine and with beta-chloro-L-alanine. Moreover, the mutant enzymes, unlike the wild type alpha 2 beta 2 complex, undergo irreversible substrate-induced inactivation. The mechanism of inactivation appears to be analogous to that first demonstrated by Metzler's group for inhibition of two other pyridoxal phosphate enzymes. Alkaline treatment of the inactivated enzyme yields apoenzyme and a previously described pyridoxal phosphate derivative. We demonstrate for the first time that enzymatic activity can be recovered by addition of pyridoxal phosphate following alkaline treatment. We conclude that the wild type and mutant alpha 2 beta 2 complexes differ in the way they process the amino acrylate intermediate. We suggest that the wild type beta subunit undergoes a conformational change upon association with the alpha subunit that alters the reaction specificity and that the mutant beta subunits do not undergo the same conformational change upon subunit association.

Structure of NADH peroxidase from Streptococcus faecalis 10C1 refined at 2.16 A resolution

The crystal structure of NADH peroxidase (EC 1.11.1.1) from Streptococcus faecalis 10C1 (Enterococcus faecalis) has been refined to a resolution of 2.16 A using the simulated annealing method. The final crystallographic R-factor is 17.7% for all data in the resolution range 7 to 2.16 A. The standard deviations are 0.015 A in bond lengths and 3.0 degrees in bond angles for the final model, which includes all 447 amino acid residues, one FAD and 369 water molecules. The enzyme is a symmetrical tetramer with point group D2; the symmetry is crystallographic. The redox center of the enzyme consists of FAD and a cysteine (Cys42), which forms a sulfenic acid (Cys-SOH) in its oxidized state. A histidine (His10) close to Cys42 is likely to act as an active-site base. In the analyzed crystal, the enzyme was in a non-native oxidation state with Cys42 oxidized to a sulfonic acid Cys-SO3H. The chain fold of NADH peroxidase is similar to those of disulfide oxidoreductases. A comparison with glutathione reductase, a representative of this enzyme family, is given.

Dracunculiasis: an approach to hasten worm expulsion

Twenty patients with Guinea worm disease having a total of 29 emerging worms in a rural village of North West Frontier Province, were put on a 5-day course of antibiotics and antiinflammatory drugs and compared with age-matched control patients. The ulcer sites of emerging worms were kept continuously moist, and 18 worms were extracted from 14 patients during the above mentioned period. The average time taken for the entire worm to be expelled in these patients was considerably shorter (13.6 days) than in controls (89 days). Seven (39%) of these worms were expelled spontaneously whereas the remaining 11 (61%) were pulled out manually with relative ease. Fifteen (75%) patients in this study had a single emerging worm, three (15%) had two emerging worms and two (10%) patients had four or more emerging worms.

Imaging objects hidden in scattering media using a fluorescence-absorption technique

A novel imaging technique is introduced to enhance the quality of an image of an object hidden in a highly scattering medium. In this technique, the object is made luminous, and its luminescent light is selected for imaging while the illuminating light is filtered out. The quality of the image can be further improved by selecting the portion of the luminescence spectrum that is strongly absorbed by the random medium.

On the feasibility of generating cw argon laser pumped energy transfer dye laser emission in the near IR spectral region

A theoretical model which predicts the dependence of the gain spectrum of cw laser pumped energy transfer dye lasers (ETDLs) on acceptor and donor concentrations as well as energy transfer parameters is developed. This model takes into account contributions resulting from both radiative and nonradiative energy transfer. Analysis of the relevant gain parameters of cw ETDLs, together with a discussion of a practically useful donor-acceptor pair, is also presented. The method developed can be used to manipulate the performance of cw laser pumped ETDLs by changing one or more of the relevant gain parameters which are contained in the gain equation. The method is also particularly promising for predicting potentially tunable cw argon laser pumped ETDL emission in the near IR spectral region.

Patterns in 51chromium red cell survival and sequestration studies

Patients with haemolytic anaemias of different etiologies were investigated using the 51Cr red cell survival and surface counting technique. The study provided definitive information regarding the presence of a haemolytic process and was found useful in the estimation of the rate as well as in the demonstration of the principal site of red cell destruction. The study also proved valuable in predicting the response to splenectomy.

Reflectance of an absorbing medium for incident light of arbitrary polarization: correlation between the oscillatory behavior and the complex plane

The reflectance of an absorbing medium R(theta)(ø) for incident light of an arbitrary state of polarization is considered as a function of the compex dielectic constant epsilon; ø is the angle incidence and theta is an incident polarization parameter, for which cos(2)theta and sin(2)theta give the power fractions of incident radiation that are p- and s-polarized, respectively. Our objective is to explore the complex epsilon-plane and define the domains for which the different types of R(theta)(ø) vs ø curves (monotonic, single minimum, and secondary maximum and minimum) occur. An ethanolic solution of Rhodamine B, an organic laser dye luminofor with a well-defined resonance absorption spectrum, was chosen as the absorbing medium. We were able to define the criteria for three distinctly different types of behavior of R(theta)(ø).

Practical method for obtaining spectral distribution of gain in energy transfer dye lasers: comparison of theory and experiment

A general theoretical model which permits theoretical predictions of the total transfer efficiency and hence identification of the appropriate energy transfer mechanisms responsible for gain enhancement in energy transfer dye lasers is developed. This model takes into account contributions due to both radiative and nonradiative transfer as well as contributions due to direct excitation of the acceptor. The theoretical predictions derived are compared with the experimental results of a laser dye mixture composed of coumarin 1 (donor) and acriflavine (acceptor) and are shown to be in excellent agreement with experimental results. The method developed is shown to be effective for predicting laser gain line shapes (and hence tunability) as well as fluorescence emission spectra of dye mixtures.

Examination of temperature effects on the lasing characteristics of rhodamine cw dye lasers

Experimental investigations on the temperature dependence of fluorescence and lasing characteristics of cw circulating organic dye lasers, excited with the multimode output of an Argon laser, were carried out for Rhodamine B, Rhodamine 6G, and Rhodamine 110 laser solutions in ethylene glycol. Significant improvements in the performance of Rhodamine B were observed as the solvent temperature was reduced below room temperature. These included significant reduction in the threshold pump requirements and a considerable increase in the attainable output power. This is in contrast to the results obtained for Rhodamine 6G and Rhodamine 110. Analysis of the results permit classification of dye lasers into three categories in so far as effects of cooling are concerned.

The structure of NADH peroxidase from Streptococcus faecalis at 3.3 A resolution

NADH peroxidase (EC 1.11.1.1) previously isolated from Streptococcus faecalis 10C1 has been crystallized. The crystal structure has been solved by multiple isomorphous replacement and solvent-flattening at 3.3 A (1 A = 0.1 nm) resolution. The enzyme forms a tetramer consisting of 4 crystallographically related subunits. The monomer chain fold is in general similar to those of glutathione reductase and lipoamide dehydrogenase. FAD binds in the same region and in a similar conformation as in glutathione reductase. The unusual cysteine-sulfenic acid participating in catalysis is located at the isoalloxazine of FAD.

Sex hormones and the immune system--Part 2. Animal data

Sex hormones have physiological and pathological (autoimmune conditions) effects on the immune system. Studies in experimental animal models of human autoimmune diseases have clearly shown that sex hormones regulate the expression, severity and course of autoimmune diseases. Sex hormones affect the function of T, B and NK cells, and macrophages. Precisely how sex hormones affect lymphocytes is a highly complex question. Sex hormones can modulate the immune system, perhaps directly (e.g. thymic reticular tissue), or indirectly via host and many oestrogen target tissues, including the central nervous system hypothalamic-pituitary axis (the neuroendocrine tissues). The effects of sex hormones on the immune system (immunosuppression or immunopotentiation) may vary, even with the same hormone. For example, oestrogen can increase IgA levels in the uterus, but decrease IgA levels in the vagina or have no effect in lacrimal tissues (Sullivan, 1989). Therefore the effects of sex hormones on the immune system cannot be generalized but must be evaluated independently. Some of the reasons for variability in results have been reviewed in detail elsewhere (Steinberg et al, 1979; Ansar Ahmed et al, 1985b). These include, dose of hormones, age and sex-hormonal status of animals, route and time of administration, the immunocompetence of the host, stress, the metabolism of hormones (e.g. metabolism of testosterone to oestrogen) resulting in alteration of biological activity, and differential response to various antigens. The initial encounter of sex hormones with the type of target cells, the variability of secondary messengers and gene activation events are other important considerations. The effects of sex hormones on the immune system to modulate immune responses are unequivocal. The burgeoning advances in cellular immunology, endocrinology and molecular biology, should provide a better understanding of: (1) the interactions of hormones with the immune system; (2) how hormones activate specific genes; and (3) how hormones influence intracellular communication. In a clinical situation, it is hoped that androgenic compounds which lack virilizing effects, but possessing the desired immunomodulatory effects, will eventually be synthesized. These hormone analogues, in combination with specific (non-toxic) oestrogen antagonists, may offer new therapeutic avenues.